Uniform Plate Slot Contacts for Improving Performance in Phase-Change Material (PCM) Radio Frequency (RF) Switches

ABSTRACT

A radio frequency (RF) switch includes a phase-change material (PCM) and a heating element underlying an active segment of the PCM, the PCM and heating element being situated over a substrate. A contact dielectric is over the PCM. PCM contacts have upper portions and uniform plate slot lower portions. The uniform plate slot lower portions have a total plate resistance R PLATE , and a total plate slot interface resistance R PLATE-INT . The upper portions have a total capacitance C UPPER  to the uniform plate slot lower portions, and the PCM has a total capacitance C PCM  to the substrate. The uniform plate slot lower portions significantly reduce a product of (R PLATE +R PLATE-INT ) and (C UPPER +C PCM ). As an alternative to the uniform plate slot lower portions, PCM contacts have segmented lower portions. The segmented lower portions significantly reduce C UPPER .

CLAIMS OF PRIORITY

The present application is a continuation-in-part of and claims thebenefit of and priority to application Ser. No. 16/103,490 filed on Aug.14, 2018, titled “Manufacturing RF Switch Based on Phase-ChangeMaterial,” Attorney Docket No. 0150200. The present application is alsoa continuation-in-part of and claims the benefit of and priority toapplication Ser. No. 16/103,587 filed on Aug. 14, 2018, titled “Designfor High Reliability RF Switch Based on Phase-Change Material,” AttorneyDocket No. 0150201. The present application is also acontinuation-in-part of and claims the benefit of and priority toapplication Ser. No. 16/103,646 filed on Aug. 14, 2018, titled “PCM RFSwitch Fabrication with Subtractively Formed Heater,” Attorney DocketNo. 0150202. The present application is further a continuation-in-partof and claims the benefit of and priority to application Ser. No.16/114,106 filed on Aug. 27, 2018, titled “Fabrication of Contacts in anRF Switch Having a Phase-Change Material (PCM) and a Heating Element,”Attorney Docket No. 0150213. The present application is further acontinuation-in-part of and claims the benefit of and priority toapplication Ser. No. 16/185,620 filed on Nov. 9, 2018, titled“Phase-Change Material (PCM) Contacts with Slot Lower Portions andContact Dielectric for Reducing Parasitic Capacitance and ImprovingManufacturability in PCM RF Switches.” Attorney Docket No. 0150206. Thedisclosures and contents of all of the above-identified applications arehereby incorporated fully by reference into the present application.

BACKGROUND

Phase-change materials (PCM) are capable of transforming from acrystalline phase to an amorphous phase. These two solid phases exhibitdifferences in electrical properties, and semiconductor devices canadvantageously exploit these differences. Given the ever-increasingreliance on radio frequency (RF) communication, there is particular needfor RF switching devices to exploit phase-change materials. However, thecapability of phase-change materials for phase transformation dependsheavily on how they are exposed to thermal energy and how they areallowed to release thermal energy. For example, in order to transforminto an amorphous phase, phase-change materials may need to achievetemperatures of approximately seven hundred degrees Celsius (700° C.) ormore, and may need to cool down within hundreds of nanoseconds.

Heating elements in PCM RF switches often contribute to parasitics, suchas parasitic capacitors, associated with RF frequencies and result inperformance tradeoffs. Additionally, the performance of an RF switchusing PCM depends heavily on how contacts to the PCM are made.Fabricating contacts to the PCM without significant RF performancetradeoffs becomes complex, especially where the RF switch is designedprimarily around thermal performance. Fabrication techniques applicableto conventional semiconductor devices may not be suitable forfabricating PCM RF switches. Accordingly, accommodating PCM in RFswitches can present significant manufacturing challenges. Specialtymanufacturing is often impractical, and large scale manufacturinggenerally trades practicality for the ability to control devicecharacteristics and critical dimensions.

Thus, there is a need in the art to reliably manufacture PCM RF switcheshaving improved RF performance.

SUMMARY

The present disclosure is directed to phase-change material (PCM)contact configurations for improving performance in PCM RF switches,substantially as shown in and/or described in connection with at leastone of the figures, and as set forth in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a cross-sectional view of a portion of a phase-changematerial (PCM) radio frequency (RF) switch.

FIG. 2 illustrates a cross-sectional view of a portion of a PCM RFswitch according to one implementation of the present application.

FIG. 3A illustrates a perspective view of a portion of a PCM RF switchaccording to one implementation of the present application.

FIG. 3B illustrates a top view of a portion of a PCM RF switchcorresponding to the PCM RF switch of FIG. 3A according to oneimplementation of the present application.

FIG. 4 illustrates a cross-sectional view of a portion of a PCM RFswitch according to one implementation of the present application.

FIG. 5A illustrates a perspective view of a portion of a PCM RF switchaccording to one implementation of the present application.

FIG. 5B illustrates a top view of a portion of a PCM RF switchcorresponding to the PCM RF switch of FIG. 5A according to oneimplementation of the present application.

FIG. 6A illustrates a perspective view of a portion of a PCM RF switchaccording to one implementation of the present application.

FIG. 6B illustrates a top view of a portion of a PCM RF switchcorresponding to the PCM RF switch of FIG. 6A according to oneimplementation of the present application.

FIG. 7A illustrates a perspective view of a portion of a PCM RF switchaccording to one implementation of the present application.

FIG. 7B illustrates a top view of a portion of a PCM RF switchcorresponding to the PCM RF switch of FIG. 7A according to oneimplementation of the present application.

FIG. 8A illustrates a perspective view of a portion of a PCM RF switchaccording to one implementation of the present application.

FIG. 8B illustrates a top view of a portion of a PCM RF switchcorresponding to the PCM RF switch of FIG. 8A according to oneimplementation of the present application.

DETAILED DESCRIPTION

The following description contains specific information pertaining toimplementations in the present disclosure. The drawings in the presentapplication and their accompanying detailed description are directed tomerely exemplary implementations. Unless noted otherwise, like orcorresponding elements among the figures may be indicated by like orcorresponding reference numerals. Moreover, the drawings andillustrations in the present application are generally not to scale, andare not intended to correspond to actual relative dimensions.

FIG. 1 illustrates a cross-sectional view of a portion of a phase-changematerial (PCM) radio frequency (RF) switch. As shown in FIG. 1, PCM RFswitch 100 includes substrate 102, lower dielectric 104, heating element106, thermally conductive and electrically insulating layer 108, PCM 110having active segment 112 and passive segments 114, PCM contacts 116,and upper dielectric.

Substrate 102 is situated under lower dielectric 104. In oneimplementation, substrate 102 is an insulator, such as silicon oxide(SiO₂). In various implementations, substrate 102 is a silicon (Si),silicon-on-insulator (SOI), sapphire, complementarymetal-oxide-semiconductor (CMOS), bipolar CMOS (BiCMOS), or group 1I-Vsubstrate. In various implementations, a heat spreader is integratedwith substrate 102, or substrate 102 itself performs as a heat spreader.Substrate 102 can have additional layers (not shown in FIG. 1). In oneimplementation, substrate 102 can comprise a plurality of interconnectmetal levels and interlayer dielectric layers. Substrate 102 can alsocomprise a plurality of devices, such as integrated passive devices(IPDs) (not shown in FIG. 1).

Lower dielectric 104 in PCM RF switch 100 is situated on top ofsubstrate 102. As shown in FIG. 1, lower dielectric 104 is also adjacentto sides of heating element 106. Lower dielectric 104 may comprise amaterial with thermal conductivity lower than that of thermallyconductive and electrically insulating layer 108. In variousimplementations, lower dielectric 104 can comprise silicon oxide (SiO₂),silicon nitride (SiN), or another dielectric.

Heating element 106 in PCM RF switch 100 is situated in lower dielectric104. Heating element 106 also underlies active segment 112 of PCM 110.Heating element 106 generates a crystallizing heat pulse or anamorphizing heat pulse for transforming active segment 112 of PCM 110.Heating element 106 can comprise any material capable of Joule heating.Heating element 106 can be connected to electrodes of a current source(not shown in FIG. 1) that generates a crystallizing current pulse or anamorphizing current pulse. Preferably, heating element 106 comprises amaterial that exhibits minimal electromigration or substantially noelectromigration. In various implementations, heating element 106 cancomprise a metal such as tungsten (W), molybdenum (Mo), titanium (Ti),titanium tungsten (TiW), titanium nitride (TiN), tantalum (Ta), nickelchromium (NiCr), or nickel chromium silicon (NiCrSi). For example, inone implementation, heating element 106 comprises tungsten lined withtitanium and titanium nitride.

Thermally conductive and electrically insulating layer 108 in PCM RFswitch 100 is situated on top of heating element 106 and lowerdielectric 104, and under PCM 110 and, in particular, under activesegment 112 of PCM 110. Thermally conductive and electrically insulatinglayer 108 ensures efficient heat transfer from heating element 106toward active segment 112 of PCM 110, while impeding electrical signalsfrom leaking out from PCM contacts 116 to heating element 106 or toother neighboring structures. Thermally conductive and electricallyinsulating layer 108 can comprise any material with high thermalconductivity and high electrical resistivity. In variousimplementations, thermally conductive and electrically insulating layer108 can comprise aluminum nitride (AlN), aluminum oxide (Al_(X)O_(Y)),beryllium oxide (Be_(X)O_(Y)), silicon carbide (SiC), diamond, ordiamond-like carbon.

PCM 110 in PCM RF switch 100 is situated on top of thermally conductiveand electrically insulating layer 108. PCM 110 includes active segment112 and passive segments 114. Active segment 112 of PCM 110approximately overlies heating element 106 and is approximately definedby heating element 106. Passive segments 114 of PCM 110 extend outwardand are transverse to heating element 106, and are situatedapproximately under PCM contacts 116. As used herein, “active segment”refers to a segment of PCM that transforms between crystalline andamorphous phases, for example, in response to a crystallizing or anamorphizing heat pulse generated by heating element 106, whereas“passive segment” refers to a segment of PCM that does not make suchtransformation and maintains a crystalline phase (i.e., maintains aconductive state). With proper heat pulses and heat dissipation, activesegment 112 of PCM 110 can transform between crystalline and amorphousphases, allowing a PCM RF switch to switch between ON and OFF statesrespectively.

PCM 110 can comprise germanium telluride (Ge_(X)Te_(Y)), germaniumantimony telluride (Ge_(X)Sb_(Y)Te_(Z)), germanium selenide(Ge_(X)Se_(Y)), or any other chalcogenide. In various implementations,PCM 110 can be germanium telluride having from forty percent to sixtypercent germanium by composition (i.e., Ge_(X)Te_(Y), where 0.4≤X≤0.6and Y=1−X). The material for PCM 110 can be chosen based upon ON stateresistivity, OFF state electric field breakdown voltage, crystallizationtemperature, melting temperature, or other considerations. PCM 110 canbe provided, for example, by physical vapor deposition (PVD) sputtering,chemical vapor deposition (CVD), evaporation, or atomic layer deposition(ALD). In one implementation, PCM 110 can have a thickness ofapproximately five hundred angstroms to approximately two thousandangstroms (500 Å-2000 Å). In other implementations, PCM 110 can have anyother thicknesses. The thickness of PCM 110 can be chosen based uponsheet resistance, crystallization power, amorphization power, or otherconsiderations. It is noted that in FIG. 1, current flowing in heatingelement 106 flows substantially under active segment 112 of PCM 110.

PCM contacts 116 in PCM RF switch 100 are situated on top of passivesegments 114 of PCM 110 and thermally conductive and electricallyinsulating layer 108, and on sidewalls of PCM 110. PCM contacts 116provide RF signals to and from PCM 110. In various implementations, PCMcontacts 116 can comprise tungsten (W), copper (Cu), or aluminum (Al).Upper dielectric 118 is situated over PCM contacts 116 and over PCM 110.

Because PCM contacts 116 in PCM RF switch 100 are situated both on topof PCM 110 and on sidewalls of PCM 110, PCM contacts 116 perform as heatsinks for PCM 110. When PCM contacts 116 sink heat from PCM 110, moreheat is required from heating element 106 in order to transform activesegment 112 of PCM 110, and thus higher power is required to switchbetween ON and OFF states.

Further, PCM RF switch 100 does not optimize various figures of merit.The ON state resistance (R_(ON)) of a PCM RF switch, the OFF stateparasitic capacitance (C_(OFF)) of a PCM RF switch, and the product ofR_(ON) and C_(OFF) are figures of merit that characterize theperformance of a PCM RF switch, where lower values represent improvedperformance. In PCM RF switch 100, PCM contacts 116 in PCM RF switch 100have wide bottom surface areas situated on thermally conductive andelectrically insulating layer 108. These wide bottom surface areas ofPCM contacts 116 form relatively large parasitic capacitors with heatingelement 106, and with substrate 102 when substrate 102 includes a heatspreader, IPDs, and/or semiconductive material (not shown in FIG. 1A),and increase the total parasitic capacitance of PCM RF switch 100. Thus,PCM RF switch 100 has increased C_(OFF) and does not optimize figures ofmerit.

FIG. 2 illustrates a cross-sectional view of a portion of a PCM RFswitch according to one implementation of the present application. Asshown in FIG. 2, PCM RF switch 200 includes substrate 202, lowerdielectric 204, upper dielectric 218, heating element 206, thermallyconductive and electrically insulating layer 208, PCM 210 having activesegment 212 and passive segments 214, contact uniformity support layer240, contact dielectric 242, PCM contacts 250 having lower portions 246and upper portions 248, resistors 252 and 254, and parasitic capacitors256 and 258.

Substrate 202, lower dielectric 204, upper dielectric 218, heatingelement 206, thermally conductive and electrically insulating layer 208,and PCM 210 in PCM RF switch 200 in FIG. 2 are similar to correspondingstructures in PCM RF switch 100 in FIG. 1, and may have anyimplementations and advantages described above. PCM RF switch 200 mayinclude other structures not shown in FIG. 2.

Contact uniformity support layer 240 is situated over PCM 110. In oneimplementation, contact uniformity support layer 240 comprises siliconnitride, i.e. Si_(X)N_(Y). In another implementation contact uniformitysupport layer 240 is a bi-layer that comprises oxide and nitride, suchas SiO₂ under Si_(X)N_(Y). Contact uniformity support layer 240 can bedeposited, for example, by plasma enhanced CVD (PECVD) or high-densityplasma CVD (HDP-CVD). In one implementation, contact uniformity supportlayer 240 can have a thickness of approximately fifty angstroms toapproximately one thousand five hundred angstroms (50 Å-1500 Å).

In the present implementation, forming lower portions 246 of PCMcontacts 250 may comprise two different etching actions. In the firstetching action, contact dielectric 242 can be aggressively etchedwithout having to accurately time the etching action. This etchingaction can use a selective etch, for example, a fluorine-based plasmadry etch, and contact uniformity support layer 240 can perform as anetch stop while contact dielectric 242 is selectively etched. In thesecond etching action, contact uniformity support layer 240 ispunch-through etched. As used herein, “punch-through” refers to a shortetching action that can be accurately timed to stop at the top surfaceof PCM 210. In PCM RF switch 200, lower portions 246 are narrow andcontact uniformity support layer 240 is thin. Thus, only a small volumeof contact uniformity support layer 240 is etched, and the punch-throughetching action is short and can be accurately timed. In oneimplementation, a chlorine-based plasma dry etch is used for thisetching action. Contact uniformity support layer 240 is optional in thatthe inventive concepts of the present application may be implementedwithout contact uniformity support layer 240, and lower portions 246 canextend through contact dielectric 242 into PCM 210. Because the R_(ON)of PCM RF switch 200 depends heavily on the uniformity of contact madebetween PCM contacts 250 and PCM 210, the R_(ON) will be significantlylower when contact uniformity support layer 240 is used.

Contact dielectric 242 is formed over PCM 210 and over contactuniformity support layer 240 (in case contact uniformity support layer240 is used). Notably, contact dielectric 242 is also formed overthermally conductive and electrically insulating layer 208. In variousimplementations, contact dielectric 242 is SiO₂, boron-doped SiO₂,phosphorous-doped SiO₂, Si_(X)N_(Y), or another dielectric. In variousimplementations, contact dielectric 242 is a low-k dielectric, such asfluorinated silicon dioxide, carbon-doped silicon oxide, or spin-onorganic polymer. Contact dielectric 242 can be formed, for example, byPECVD, HDP-CVD, or spin-on processes. In one implementation, thethickness of contact dielectric 242 can range from approximately onehalf a micron to approximately two microns (0.5 μm-2 μm). In otherimplementations, contact dielectric 242 can have any other thicknesses.In one implementation, a thickness of contact dielectric 242 issignificantly greater than a thickness of thermally conductive andelectrically insulating layer 208. In one implementation, a thickness ofcontact dielectric 242 is significantly greater than a thickness ofcontact uniformity support layer 240.

Lower portions 246 of PCM contacts 250 extend through contact dielectric242 and through contact uniformity support layer 240 (in case contactuniformity support layer 240 is used), and connect to passive segments214 of PCM 210. Notably, lower portions 246 are narrow and connect tothe top of PCM 210, not to the sidewalls of PCM 210. In oneimplementation, a metal layer is deposited in and over contactdielectric 242, and then planarized with contact dielectric 242, forexample, using chemical machine polishing (CMP), thereby forming lowerportions 246. In an alternative implementation, a single damasceneprocess is used to form lower portions 246. In various implementations,lower portions 246 can comprise W, Al, or Cu. Lower portions 246 arepart of PCM contacts 250 that provide RF signals to and from PCM 210. Asdescribed below, lower portions 246 can be uniform plate slot lowerportions, or segmented lower portions.

Upper portions 248 are situated over contact dielectric 242 and overlower portions 246. Together, lower portions 246 and upper portions 248make up PCM contacts 250 that provide RF signals to and from PCM 210.Upper portions 248 facilitate external connections for PCM RF switch 200and also improve signal handling. In one implementation, a metal layeris deposited over contact dielectric 242 and over lower portions 246,and then a middle segment thereof overlying active segment 212 isetched, thereby forming upper portions 248. In an alternativeimplementation, a single damascene process is used to form upperportions 248. In various implementations, upper portions 248 cancomprise W, Al, or Cu. In one implementation, lower portions 246 cancomprise W, and upper portions 248 can comprise Al or Cu.

Although lower portions 246 and upper portions 248 are separateformations in FIG. 2, in other implementations they may be parts of thesame formation. For example, lower portions 246 and upper portions 248can be formed as a single metal using a dual damascene process. Asanother example, lower portions 246 and upper portions 248 can be formedas a single metal by depositing a metal layer in and over contactdielectric 242, and then etching a middle segment thereof overlyingactive segment 212. Notably, in these examples, lower portions 246 andupper portions 248 would not have a boundary interface. Although lowerportions 246 and upper portions 248 are aligned in FIG. 2, in variousimplementations, upper portions 248 can have an offset towards activesegment 212 of PCM 210 or can have an offset away from active segment212 of PCM 210.

Utilizing contact dielectric 242 along with lower portions 246 and upperportions 248 of PCM contacts 250 improves both the thermal performanceand the RF performance of PCM RF switch 200. Compared to PCM contacts116 in FIG. 1, PCM contacts 250 in FIG. 2 have significantly reducedparasitic capacitance. Because contact dielectric 242 is situated overthermally conductive and electrically insulating layer 208, the widebottom surface areas of upper portions 248 have increased separationfrom heating element 206 and substrate 202, and parasitic capacitance isreduced. In one implementation, parasitic capacitance of PCM RF switch100 in FIG. 1 is approximately ten femto-Farads (10 fF), while parasiticcapacitance of PCM RF switch 200 in FIG. 2 is approximately between ahalf of a femto-Farad and two femto-Farads (0.5 fF-2.0 fF).

Additionally, the thickness of contact dielectric 242 can be increasedin order to reduce parasitic capacitance, without impacting heattransfer from heating element 206 to active segment 212 of PCM 210.Moreover, because contact dielectric 242 adjoins the sidewalls of PCM210 and narrow lower portions 246 connect to the top of PCM 210, PCMcontacts 250 do not sink significant amounts of heat from PCM 210. Lessheat is required from heating element 206 in order to transform activesegment 212 of PCM 210, and thus less power is required to switchbetween ON and OFF states.

Resistors 252 are formed by the interfaces of lower portions 246 andpassive segments 214 of PCM 210. As described below, resistors 252 canrepresent a total plate slot interface resistance (R_(PLATE-INT)) or atotal segmented interface resistance (R_(SEG-INT)). The resistancevalues of resistors 252 are generally governed by the materials of lowerportions 246 and PCM 210, the dimensions of their interfaces, and theuniformity of contact at their interfaces. Accordingly, the resistancevalues of resistors 252 will be significantly lower when contactuniformity support layer 240 is used. Resistors 254 are formed by lowerportions 246. As described below, resistors 254 can represent a totalplate resistance (R_(PLATE)) or a total segmented resistance (R_(SEG)).The resistance values of resistors 254 are generally governed by thematerial of lower portions 246 and the dimensions of lower portions 246.Resistors 252 and resistors 254 both contribute to the total R_(ON) ofPCM RF switch 200. Notably, in FIG. 2 lower portions 246 of PCM contacts250 are narrow. In one implementation, the width of lower portions 246of PCM contacts 250 can be a minimum process size.

Parasitic capacitors 256 are formed between PCM 210 and substrate 202.Parasitic capacitors 256 together represent a total capacitance(C_(PCM)) of PCM 210 to substrate 202. The capacitance values ofparasitic capacitors 256 are generally governed by the dimensions of PCM210 and substrate 202, the distance between them, and the materialbetween them. Parasitic capacitors 258 are formed between upper portions248 and opposite lower portions 246. As described below, parasiticcapacitors 258 can represent a total capacitance (C_(UPPER)) of upperportions 248 to uniform plate slot lower portions, or to segmented lowerportions. The capacitance values of parasitic capacitors 258 aregenerally governed by the dimensions of upper portions 248 and lowerportions 246, the distance between them, and the material between them.Parasitic capacitors 256 and parasitic capacitors 258 both contribute tothe total Con, of PCM RF switch 200.

FIG. 3A illustrates a perspective view of a portion of a PCM RF switchaccording to one implementation of the present application. PCM RFswitch 200 in FIG. 2 can represent a cross-sectional view along line“2-2” of PCM RF switch 300A in FIG. 3A. As shown in FIG. 3A, PCM RFswitch 300A includes substrate 302, lower dielectric 304, heatingelement 306, thermally conductive and electrically insulating layer 308,PCM 310 having active segment 312 and passive segments 314, PCM contacts350 having uniform plate slot lower portions 346 and upper portions 348,resistors 352 and 354, and parasitic capacitors 356 and 358. Heatingelement 306 is illustrated with dashed lines as seen through variousstructures of PCM RF switch 300A.

Substrate 302, lower dielectric 304, heating element 306, thermallyconductive and electrically insulating layer 308, and PCM 310 in PCM RFswitch 300A in FIG. 3A are similar to corresponding structures in PCM RFswitch 200 in FIG. 2, and may have any implementations and advantagesdescribed above. PCM RF switch 300A may include other structures notshown in FIG. 3A, such as a contact uniformity support layer or acontact dielectric.

PCM RF switch 300A includes PCM contacts 350 having uniform plate slotlower portions 346. As used herein, “slot” refers to the lengths oflower portions 346 in the direction parallel to heating element 306being significantly greater than the widths of lower portions 346 in thedirection transverse to heating element 306. In one implementation, thelengths of lower portions 346 are at least twenty times greater thantheir widths. Thus, lower portions 346 appear to create slots betweenupper portions 348 and passive segments 314 of PCM 310. As used herein,“uniform plate” refers to lower portions 346 being substantiallycontinuous, rather than segmented.

Resistor 352 represents the resistance between one of uniform plate slotlower portions 346 and one of passive segments 314 of PCM 310. Resistor352 represents half of the total plate slot interface resistance(R_(PLATE-INT)) of uniform plate slot lower portions 346. Anotherresistor (not shown in FIG. 3A) corresponding to the other one ofuniform plate slot lower portions 346 would represent to other half ofthe total plate slot interface resistance (R_(PLATE-INT)).

Resistor 354 represents the resistance of one of uniform plate slotlower portions 346. Resistor 354 represents half of the total plateresistance (R_(PLATE)) of uniform plate slot lower portions 346. Anotherresistor (not shown in FIG. 3A) corresponding to the other one ofuniform plate slot lower portions 346 would represent the other half ofthe total plate resistance (R_(PLATE)).

Parasitic capacitor 356 represents half of the total capacitance(C_(PCM)) of PCM 310 to substrate 302. Another parasitic capacitor 356(not shown in FIG. 3A) would represents the other half of the totalcapacitance (C_(PCM)) of PCM 310 to substrate 302. The two parasiticcapacitors 356 (only one of which is shown in FIG. 3A) together wouldrepresent the total capacitance (C_(PCM)) of PCM 310 to substrate 302.Parasitic capacitor 358 represents the capacitance of one of upperportions 348 to an opposite one of uniform plate slot lower portions346. Parasitic capacitor 358 represents half of the total capacitance(C_(UPPER)) of upper portions 348 to uniform plate slot lower portions346. Another parasitic capacitor (not shown in FIG. 3A) corresponding tothe other one of upper portions 348 would represent the other half ofthe total capacitance (C_(UPPER)) of upper portions 348.

PCM contacts 350 having uniform plate slot lower portions 346significantly reduce a product of (R_(PLATE)+R_(PLATE-INT)) and(C_(UPPER)+C_(PCM)). Because uniform plate slot lower portions 346 arecontinuous uniform plates and relatively long slots, both R_(PLATE) andR_(PLATE-INT) are reduced. Also because uniform plate slot lowerportions 346 are continuous uniform plates and relatively long slots,current crowding is reduced at corners of uniform plate slot lowerportions 346 nearest active segment 312 of PCM 310. R_(PLATE-INT) isfurther reduced where contact uniformity support layer 240 (shown inFIG. 2) is used. Moreover, as described below, because uniform plateslot lower portions 346 are narrow plates, the area of PCM 310 isreduced, thus reducing C_(PCM). Significantly reducing the product of(R_(PLATE)+R_(PLATE-INT)) and (C_(UPPER)+C_(PCM)) in PCM RF switch 300Acorrespondingly reduces the product of R_(ON) and C_(OFF) figure ofmerit, improving characteristic performance of PCM RF switch 300A.

FIG. 3B illustrates a top view of a portion of a PCM RF switchcorresponding to the PCM RF switch of FIG. 3A according to oneimplementation of the present application. Only PCM 310 and uniformplate slot lower portions 346 are shown in the top view of PCM RF switch300B in FIG. 3B.

Width W₁ between respective uniform plate slot lower portions 346represents the width of the active segment of PCM RF switch 300B. WidthW₁ can be given as a design criteria. Width W₂ is the width of one ofuniform plate slot lower portions 346. In the present implementation,width W₂ is small, and uniform plate slot lower portions 346 are narrowplates. In one implementation, width W₂ can be a minimum process size.Width W₃ is the width of the entire PCM 310 (i.e. the combined widths ofthe active segment and the passive segments of the PCM). As shown inFIG. 3B, width W₃ of PCM 310 is approximately equal to width W₁ plus thewidths of uniform plate slot lower portions 346, plus any margin oferror needed for forming uniform plate slot lower portions 346(W₃≈W₁+2W₂). Because uniform plate slot lower portions 346 are narrowplates, the width W₃ of PCM 310 is minimized. The area of PCM 310 isthus reduced, in turn reducing C_(PCM) (i.e., reducing parasiticcapacitors 256 in FIG. 2).

FIG. 4 illustrates a cross-sectional view of a portion of a PCM RFswitch according to one implementation of the present application. Asshown in FIG. 4, PCM RF switch 400 includes substrate 402, lowerdielectric 404, upper dielectric 418, heating element 406, thermallyconductive and electrically insulating layer 408, PCM 410 having activesegment 412 and passive segments 414, contact uniformity support layer440, contact dielectric 442, PCM contacts 450 having lower portions 446and upper portions 448, resistors 452 and 454, and parasitic capacitors456 and 458.

Substrate 402, lower dielectric 404, upper dielectric 418, heatingelement 406, thermally conductive and electrically insulating layer 408,PCM 410, contact uniformity support layer 440, contact dielectric 442,resistors 452 and 454, and parasitic capacitors 456 and 458 in PCM RFswitch 400 in FIG. 4 are similar to corresponding structures in PCM RFswitch 200 in FIG. 2, and may have any implementations and advantagesdescribed above. PCM RF switch 400 may include other structures notshown in FIG. 4.

Lower portions 446 of PCM contacts 450 in FIG. 4 are wider than lowerportions 246 of PCM contact 250 in FIG. 2. In various implementations,the width of lower portions 446 of PCM contacts 450 can be twice aminimum process size or wider. The width of PCM 410 in FIG. 4, whichlower portions 446 connect to, is also wider than the width of PCM 210in FIG. 2. As described below, lower portions 446 can be uniform plateslot lower portions, or segmented lower portions. Also as describedbelow, where lower portions 446 are wider, the resistance values ofresistors 452 and 454 are reduced, reducing R_(PLATE) and R_(PLATE-INT),or reducing R_(SEG) and R_(SEG-INT).

FIG. 5A illustrates a perspective view of a portion of a PCM RF switchaccording to one implementation of the present application. PCM RFswitch 400 in FIG. 4 can represent a cross-sectional view along line“4-4” of PCM RF switch 500A in FIG. 5A. As shown in FIG. 5A, PCM RFswitch 500A includes substrate 502, lower dielectric 504, heatingelement 506, thermally conductive and electrically insulating layer 508,PCM 510 having active segment 512 and passive segments 514, PCM contacts550 having uniform plate slot lower portions 546 and upper portions 548,resistors 552 and 554, and parasitic capacitors 556 and 558. Heatingelement 506 is illustrated with dashed lines as seen through variousstructures of PCM RF switch 500A.

Substrate 502, lower dielectric 504, heating element 506, thermallyconductive and electrically insulating layer 508, resistors 552 and 554,and parasitic capacitors 556 and 558 in PCM RF switch 500A in FIG. 5Aare similar to corresponding structures in PCM RF switch 300A in FIG.3A, and may have any implementations and advantages described above. PCMRF switch 500A may include other structures not shown in FIG. 5A, suchas a contact uniformity support layer or a contact dielectric. Notably,PCM 510 and uniform plate slot lower portions 546 of PCM contacts 550 inFIG. 5A are wider than their corresponding structures in FIG. 3A.

PCM contacts 550 having uniform plate slot lower portions 546significantly reduce a product of (R_(PLATE)+R_(PLATE-INT)) and(C_(UPPER)+C_(PCM)). Because uniform plate slot lower portions 546 arecontinuous uniform plates and relatively long slots, both R_(PLATE) andR_(PLATE-INT) are reduced. Also because uniform plate slot lowerportions 546 are continuous uniform plates and relatively long slots,current crowding is reduced at corners of uniform plate slot lowerportions 546 nearest active segment 512 of PCM 510. R_(PLATE-INT) isfurther reduced where contact uniformity support layer 240 (shown inFIG. 2) is used. Moreover, as described below, because uniform plateslot lower portions 546 are wide plates, both R_(PLATE) andR_(PLATE-INT) are further reduced. Significantly reducing the product of(R_(PLATE)+R_(PLATE-INT)) and (C_(UPPER)+C_(PCM)) in PCM RF switch 500Acorrespondingly reduces the product of R_(ON) and C_(OFF) figure ofmerit, improving characteristic performance of PCM RF switch 500A.

FIG. 5B illustrates a top view of a portion of a PCM RF switchcorresponding to the PCM RF switch of FIG. 5A according to oneimplementation of the present application. Only PCM 510 and uniformplate slot lower portions 546 are shown in the top view of PCM RF switch500B in FIG. 5B.

Width W₁ between respective uniform plate slot lower portions 546represents the width of the active segment of PCM RF switch 500B. WidthW₁ can be given as a design criteria. Width W₄ is the width of one ofuniform plate slot lower portions 546. In the present implementation,width W₄ is large, and uniform plate slot lower portions 546 are wideplates. In one implementation, width W₄ can be twice a minimum processsize or wider. Width W₅ is the width of the entire PCM 510. As shown inFIG. 5B, width W₅ of PCM 510 is approximately equal to width W₁ plus thewidths of uniform plate slot lower portions 546, plus any margin oferror needed for forming uniform plate slot lower portions 546(W₅≈W₁+2W₄). Because uniform plate slot lower portions 546 are wideplates, R_(PLATE) is reduced. Also because uniform plate slot lowerportions 546 are wide plates, the interface area of uniform plate slotlower portions 546 and PCM 510 is reduced, reducing R_(PLATE-INT) (i.e.,reducing resistors 454 and 452 in FIG. 4). It is noted that the totalresistance represented by R_(PLATE)+R_(PLATE-INT) is lower in theimplementation of FIGS. 5A/5B relative to R_(PLATE)+R_(PLATE-INT) in theimplementation of FIGS. 3A/3B. However, due to the fact that width W₅ ofPCM 510 in the implementation of FIGS. 5A/5B is greater than width W₃ ofPCM 310 in the implementation of FIGS. 3A/3B, parasitic capacitors 556(i.e. total capacitance (C_(PCM)) of PCM 510 to substrate 502) aregreater than parasitic capacitors 356 (i.e. total capacitance (C_(PCM))of PCM 310 to substrate 302).

FIG. 6A illustrates a perspective view of a portion of a PCM RF switchaccording to one implementation of the present application. PCM RFswitch 200 in FIG. 2 can represent a cross-sectional view along line“2-2” of PCM RF switch 600A in FIG. 6A. As shown in FIG. 6A, PCM RFswitch 600A includes substrate 602, lower dielectric 604, heatingelement 606, thermally conductive and electrically insulating layer 608,PCM 610 having active segment 612 and passive segments 614, PCM contacts650 having segmented lower portions 646 a, 646 b, 646 c. 646 d, and 646e (collectively referred to as segmented lower portions 646) and upperportions 648, resistors 652 and 654, and parasitic capacitors 656 and658. Heating element 606 is illustrated with dashed lines as seenthrough various structures of PCM RF switch 600A.

Substrate 602, lower dielectric 604, heating element 606, thermallyconductive and electrically insulating layer 608, and PCM 610 in PCM RFswitch 600A in FIG. 6A are similar to corresponding structures in PCM RFswitch 300A in FIG. 3A, and may have any implementations and advantagesdescribed above. PCM RF switch 600A may include other structures notshown in FIG. 6A, such as a contact uniformity support layer or acontact dielectric.

PCM RF switch 600A includes PCM contacts 650 having segmented lowerportions 646. As used herein. “segmented” lower portions refer to lowerportions that are not continuous and comprise multiple segments thatconnect to the PCM below and the upper portion above, and thus thesegmented lower portions are electrically shorted to each other. In FIG.6A, segmented lower portions 646 are square segments.

Resistor 652 represents the resistance between one of segmented lowerportions 646 a and one of passive segments 614 of PCM 610. In thepresent implementation, resistor 652 is combined in parallel with othersimilar resistors of other segments to result in a total segmentedinterface resistance (R_(SEG-INT)) of segmented lower portions 646. Thetotal segmented interface resistance (R_(SEG-INT)) in the example ofFIG. 6A is about one-tenth of resistance of individual resistor 652.Another resistor (not shown in FIG. 6A) corresponding to the other oneof segmented lower portions 646 a, along with other resistors (not shownin FIG. 6A) corresponding to segmented lower portions 646 b, 646 c, 646d, and 646 e, would represent the remaining resistors that combine inparallel to result in the total segmented interface resistance(R_(SEG-INT)).

Resistor 654 represents the resistance of one of segmented lowerportions 646 a. In the present implementation, resistor 654 is combinedin parallel with other similar resistors of other segments to result ina total segmented resistance (R_(SEG)) of segmented lower portions 646.The total segmented resistance (R_(SEG)) in the example of FIG. 6A isabout one-tenth of resistance of individual resistor 654. Anotherresistor (not shown in FIG. 6A) corresponding to the other one ofsegmented lower portions 646 a, along with other resistors (not shown inFIG. 6A) corresponding to segmented lower portions 646 b, 646 c, 646 d,and 646 e, would represent the remaining resistors that combine inparallel to result in the total segmented resistance (R_(SEG)).

Parasitic capacitor 656 represents half of the total capacitance(C_(PCM)) of PCM 610 to substrate 602. Another parasitic capacitor 656(not shown in FIG. 6A) would represents the other half of the totalcapacitance (C_(PCM)) of PCM 610 to substrate 602. The two parasiticcapacitors 656 (only one of which is shown in FIG. 6A) together wouldrepresent the total capacitance (C_(PCM)) of PCM 610 to substrate 602.Parasitic capacitor 658 represents the capacitance of one of upperportions 648 to an opposite one of segmented lower portions 646 a. Inthe present implementation, parasitic capacitor 658 represents about onetenth of the total capacitance (C_(UPPER)) of upper portions 648 tosegmented lower portions 646. Another parasitic capacitor (not shown inFIG. 6A) corresponding to the other one segmented lower portions 646 a,along with other parasitic capacitors (not shown in FIG. 6A)corresponding to segmented lower portions 646 b, 646 c, 646 d, and 646e, would represent the remainder of the total capacitance (C_(UPPER)) ofupper portions 648.

Because segmented lower portions 646 are not continuous, less area isavailable to capacitively couple with opposite upper portions 648,relative to uniform plate slot lower portions 346 in FIG. 3A. As aresult. PCM contacts 650 having segmented lower portions 646significantly reduce parasitic capacitance C_(UPPER) (i.e., reduceparasitic capacitors 258 in FIG. 2), relative to uniform plate slotlower portions 346 in FIG. 3A. Significantly reducing C_(UPPER) in PCMRF switch 600A correspondingly reduces the Cow figure of merit,improving characteristic performance of PCM RF switch 600A.

FIG. 6B illustrates a top view of a portion of a PCM RF switchcorresponding to the PCM RF switch of FIG. 6A according to oneimplementation of the present application. Only PCM 610 and segmentedlower portions 646 a, 646 b, 646 c, 646 d, and 646 e (collectivelyreferred to as segmented lower portions 646) are shown in the top viewof PCM RF switch 600B in FIG. 6B.

As shown in FIG. 6B, segmented lower portions 646 are square segments.In one implementation, the length and width of segmented lower portions646 can be a minimum process size. As described above, because segmentedlower portions 646 are not continuous, less area is available to coupleand parasitic capacitance C_(UPPER) is significantly reduced.

FIG. 7A illustrates a perspective view of a portion of a PCM RF switchaccording to one implementation of the present application. PCM RFswitch 200 in FIG. 2 can represent a cross-sectional view along line“2-2” of PCM RF switch 700A in FIG. 7A. As shown in FIG. 7A, PCM RFswitch 700A includes substrate 702, lower dielectric 704, heatingelement 706, thermally conductive and electrically insulating layer 708,PCM 710 having active segment 712 and passive segments 714, PCM contacts750 having segmented lower portions 746 a, 746 b, and 746 c(collectively referred to as segmented lower portions 746) and upperportions 748, resistors 752 and 754, and parasitic capacitors 756 and758. Heating element 706 is illustrated with dashed lines as seenthrough various structures of PCM RF switch 700A.

Substrate 702, lower dielectric 704, heating element 706, thermallyconductive and electrically insulating layer 708, PCM 710, resistors 752and 754, and parasitic capacitors 756 and 758 in PCM RF switch 700A inFIG. 7A are similar to corresponding structures in PCM RF switch 600A inFIG. 6A, and may have any implementations and advantages describedabove. PCM RF switch 700A may include other structures not shown in FIG.7A, such as a contact uniformity support layer or a contact dielectric.

PCM RF switch 700A includes PCM contacts 750 having segmented lowerportions 746. In FIG. 7A, segmented lower portions 746 are rectangularsegments. Segmented lower portions 746 are laid out length-wise over PCM710 (i.e., parallel to heating element 706).

Resistor 752 represents the resistance between one of segmented lowerportions 746 a and one of passive segments 714 of PCM 710. In thepresent implementation, resistor 752 is combined in parallel with othersimilar resistors of other segments to result in a total segmentedinterface resistance (R_(SEG-INT)) of segmented lower portions 746. Thetotal segmented interface resistance (R_(SEG-INT)) in the example ofFIG. 7A is about one-sixth of resistance of individual resistor 752.Another resistor (not shown in FIG. 7A) corresponding to the other oneof segmented lower portions 746 a, along with other resistors (not shownin FIG. 7A) corresponding to segmented lower portions 746 b and 746 c,would represent the remaining resistors that combine in parallel toresult in the total segmented interface resistance (R_(SEG-INT)).

Resistor 754 represents the resistance of one of segmented lowerportions 746 a. In the present implementation, resistor 754 is combinedin parallel with other similar resistors of other segments to result ina total segmented resistance (R_(SEG)) of segmented lower portions 746.The total segmented resistance (R_(SEG)) in the example of FIG. 7A isabout one-sixth of resistance of individual resistor 754. Anotherresistor (not shown in FIG. 7A) corresponding to the other one ofsegmented lower portions 746 a, along with other resistors (not shown inFIG. 7A) corresponding to segmented lower portions 746 b and 746 c,would represent the remaining resistors that combine in parallel toresult in the total segmented resistance (R_(SEG)).

Parasitic capacitor 756 represents half of the total capacitance(C_(PCM)) of PCM 710 to substrate 702. Another parasitic capacitor 756(not shown in FIG. 7A) would represents the other half of the totalcapacitance (C_(PCM)) of PCM 710 to substrate 702. The two parasiticcapacitors 756 (only one of which is shown in FIG. 7A) together wouldrepresent the total capacitance (C_(PCM)) of PCM 710 to substrate 702.Parasitic capacitor 758 represents the capacitance of one of upperportions 748 to an opposite one of segmented lower portions 746 a. Inthe present implementation, parasitic capacitor 758 represents about onesixth of the total capacitance (C_(UPPER)) of upper portions 748 tosegmented lower portions 746. Another parasitic capacitor (not shown inFIG. 7A) corresponding to the other one segmented lower portions 746 a,along with other parasitic capacitors (not shown in FIG. 7A)corresponding to segmented lower portions 746 b and 746 c, wouldrepresent the remainder of the total capacitance (C_(UPPER)) of upperportions 748.

Because segmented lower portions 746 in FIG. 7A are not continuous, lessarea is available to couple with opposite upper portions 748, relativeto uniform plate slot lower portions 346 in FIG. 3A. As a result,segmented lower portions 746 in FIG. 7A significantly reduce C_(UPPER)(i.e., reduce parasitic capacitors 258 in FIG. 2), relative to uniformplate slot lower portions 346 in FIG. 3A. Additionally, becausesegmented lower portions 746 in FIG. 7A are rectangular segments thatare laid out length-wise over PCM 710, segmented lower portions 746 arelarger, and the interface area of segmented lower portions 746 and PCM710 is larger, relative to segmented lower portions 646 in FIG. 6A. As aresult, segmented lower portions 746 in FIG. 7A reduce the total R_(SEG)and R_(SEG-INT) (i.e., reduce resistors 254 and 252 in FIG. 2), relativeto segmented lower portions 646 in FIG. 6A. Improving R_(SEG),R_(SEG-INT), and C_(UPPER) as shown in FIG. 7A can optimize a product ofR_(ON) and C_(OFF) figure of merit for PCM RF switch 700A, especiallywhere more weight is given to R_(ON), relative to PCM RF switch 600A inFIG. 6A.

It is noted that although segmented lower portions 746 in FIG. 7Asignificantly reduce C_(UPPER) (i.e., reduce parasitic capacitors 258 inFIG. 2), relative to uniform plate slot lower portions 346 in FIG. 3A,the reduction in C_(UPPER) in the configuration of FIG. 6A (i.e. usingsquare segments) is more significant than the reduction of C_(UPPER) inFIG. 7A (i.e. length-wise rectangular segments) since the total surfacearea of segmented lower portions 746 in FIG. 7A for capacitive couplingwith upper portions 748 is greater than the total surface area ofsegmented lower portions 646 in FIG. 6A for capacitive coupling withupper portions 648.

FIG. 7B illustrates a top view of a portion of a PCM RF switchcorresponding to the PCM RF switch of FIG. 7A according to oneimplementation of the present application. Only PCM 710 and segmentedlower portions 746 a, 746 b, and 746 c (collectively referred to assegmented lower portions 746) are shown in the top view of PCM RF switch700B in FIG. 7B.

As shown in FIG. 7B, segmented lower portions 746 are rectangularsegments laid out length-wise over PCM 710. In one implementation, thewidth of segmented lower portions 746 can be a minimum process size, andthe length of segmented lower portions 746 can be twice a minimumprocess size or longer. As described above, because segmented lowerportions 746 are not continuous, less area is available for capacitivecoupling and C_(upper) is significantly reduced, relative to FIG. 3A.Also as described above, because segmented lower portions 746 and theirinterface areas with PCM 710 are larger, R_(SEG) and R_(SEG-INT) arereduced relative to FIG. 6A.

FIG. 8A illustrates a perspective view of a portion of a PCM RF switchaccording to one implementation of the present application. PCM RFswitch 400 in FIG. 4 can represent a cross-sectional view along line“4-4” of PCM RF switch 800A in FIG. 8A. As shown in FIG. 8A, PCM RFswitch 800A includes substrate 802, lower dielectric 804, heatingelement 806, thermally conductive and electrically insulating layer 808,PCM 810 having active segment 812 and passive segments 814, PCM contacts850 having segmented lower portions 846 a, 846 b, 846 c, 846 d, and 846e (collectively referred to as segmented lower portions 846) and upperportions 848, resistors 852 and 854, and parasitic capacitors 856 and858. Heating element 806 is illustrated with dashed lines as seenthrough various structures of PCM RF switch 800A.

Substrate 802, lower dielectric 804, heating element 806, thermallyconductive and electrically insulating layer 808, PCM 810, resistors 852and 854, and parasitic capacitors 856 and 858 in PCM RF switch 800A inFIG. 8A are similar to corresponding structures in PCM RF switch 700A inFIG. 7A, and may have any implementations and advantages describedabove. PCM RF switch 800A may include other structures not shown in FIG.8A, such as a contact uniformity support layer or a contact dielectric.

PCM RF switch 800A includes PCM contacts 850 having segmented lowerportions 846. In FIG. 8A, segmented lower portions 846 are rectangularsegments. Segmented lower portions 846 are laid out width-wise over PCM810 (i.e., transverse to heating element 806). As described above, wherethe width of the active segment of the PCM RF switch is given as adesign criteria, wider lower portions 846 result in wider PCM 810 inFIG. 8A, relative to PCM 610 in FIG. 6A.

Resistor 852 represents the resistance between one of segmented lowerportions 846 a and one of passive segments 814 of PCM 810. In thepresent implementation, resistor 852 is combined in parallel with othersimilar resistors of other segments to result in a total segmentedinterface resistance (R_(SEG-INT)) of segmented lower portions 846. Thetotal segmented interface resistance (R_(SEG-INT)) in the example ofFIG. 8A is about one-tenth of resistance of individual resistor 852.Another resistor (not shown in FIG. 8A) corresponding to the other oneof segmented lower portions 846 a, along with other resistors (not shownin FIG. 8A) corresponding to segmented lower portions 846 b, 846 c, 846d, and 846 e would represent the remaining resistors that combine inparallel to result in the total segmented interface resistance(R_(SEG-INT)).

Resistor 854 represents the resistance of one of segmented lowerportions 846 a. In the present implementation, resistor 854 is combinedin parallel with other similar resistors of other segments to result ina total segmented resistance (R_(SEG)) of segmented lower portions 846.The total segmented resistance (R_(SEG)) in the example of FIG. 8A isabout one-tenth of resistance of individual resistor 854. Anotherresistor (not shown in FIG. 8A) corresponding to the other one ofsegmented lower portions 846 a, along with other resistors (not shown inFIG. 8A) corresponding to segmented lower portions 846 b, 846 c, 846 d,and 846 e, would represent the remaining resistors that combine inparallel to result in the total segmented resistance (R_(SEG)).

Parasitic capacitor 856 represents half of the total capacitance(C_(PCM)) of PCM 810 to substrate 802. Another parasitic capacitor 856(not shown in FIG. 8A) would represents the other half of the totalcapacitance (C_(PCM)) of PCM 810 to substrate 802. The two parasiticcapacitors 856 (only one of which is shown in FIG. 8A) together wouldrepresent the total capacitance (C_(PCM)) of PCM 810 to substrate 802.Parasitic capacitor 858 represents the capacitance of one of upperportions 848 to an opposite one of segmented lower portions 846 a. Inthe present implementation, parasitic capacitor 858 represents one tenthof the total capacitance (C_(UPPER)) of upper portions 848 to segmentedlower portions 846. Another parasitic capacitor (not shown in FIG. 8A)corresponding to the other one segmented lower portions 846 a, alongwith other parasitic capacitors (not shown in FIG. 8A) corresponding tosegmented lower portions 846 b, 846 c, 846 d, and 846 e, would representthe remainder of the total capacitance (C_(UPPER)) of upper portions848.

Because segmented lower portions 846 in FIG. 8A are not continuous, lessarea is available to couple with opposite upper portions 848, relativeto uniform plate slot lower portions 546 in FIG. 5A. As a result,segmented lower portions 846 in FIG. 8A significantly reduce C_(UPPER)(i.e., reduce parasitic capacitors 458 in FIG. 4), relative to uniformplate slot lower portions 546 in FIG. 5A. Additionally, becausesegmented lower portions 846 in FIG. 8A are rectangular segments thatare laid out width-wise over PCM 810, segmented lower portions 846 arelarger, and the interface area of segmented lower portions 846 and PCM810 is larger, relative to segmented lower portions 646 in FIG. 6A. As aresult, segmented lower portions 846 in FIG. 8A reduce R_(SEG) andR_(SEG-INT) (i.e., reduce resistors 254 and 252 in FIG. 2), relative tosegmented lower portions 646 in FIG. 6A. Improving R_(SEG), R_(SEG-INT),and C_(UPPER) as shown in FIG. 8A can optimize a product of R_(ON) andC_(OFF) figure of merit for PCM RF switch 800A, especially where moreweight is given to R_(ON), relative to PCM RF switch 600A in FIG. 6A.

FIG. 8B illustrates a top view of a portion of a PCM RF switchcorresponding to the PCM RF switch of FIG. 8A according to oneimplementation of the present application. Only PCM 810 and segmentedlower portions 846 a, 846 b, 846 c, 846 d, and 846 e (collectivelyreferred to as segmented lower portions 846) are shown in the top viewof PCM RF switch 800B in FIG. 8B.

As shown in FIG. 8B, segmented lower portions 846 are rectangularsegments laid out width-wise over PCM 810. In one implementation, thelength of segmented lower portions 846 can be a minimum process size,and the width of segmented lower portions 846 can be twice a minimumprocess size or wider. As described above, because segmented lowerportions 846 are not continuous, less area is available for capacitivecoupling and C_(UPPER) is significantly reduced, relative to FIG. 5A.Also as described above, because segmented lower portions 846 and theirinterface areas with PCM 810 are larger, R_(SEG) and R_(SEG-INT) arereduced relative to FIG. 6A.

It is noted that although segmented lower portions 846 in FIG. 8Asignificantly reduce C_(UPPER) (i.e., reduce parasitic capacitors 458 inFIG. 4), relative to uniform plate slot lower portions 546 in FIG. 5A,the reduction in C_(UPPER) in the configuration of FIG. 6A (i.e. usingsquare segments) is more significant than the reduction of C_(upper) inFIG. 8A (i.e. width-wise rectangular segments) since the total surfacearea of segmented lower portions 846 in FIG. 8A for capacitive couplingwith upper portions 848 is greater than the total surface area ofsegmented lower portions 646 in FIG. 6A for capacitive coupling withupper portions 648.

It is further noted that the width of PCM 810 in the implementation ofFIGS. 8A/8B (i.e. width-wise rectangular segments) is analogous to widthW₅ of PCM 510 in the implementation of FIGS. 5A/5B, while the width ofPCM 710 in the implementation of FIGS. 7A/7B (i.e. length-wiserectangular segments) is analogous to width W₃ of PCM 310 in theimplementation of FIGS. 3A/3B. In other words, the width of PCM 810 inthe implementation of FIGS. 8A/8B is greater than the width of PCM 710in the implementation of FIGS. 7A/7B. As a result, parasitic capacitors856 (i.e. total capacitance (C_(PCM)) of PCM 810 to substrate 802) inthe implementation of FIGS. 8A/8B are greater than parasitic capacitors756 (i.e. total capacitance (C_(PCM)) of PCM 710 to substrate 702) inthe implementation of FIGS. 7A/7B.

Thus, in various implementations of the present application, PCM RFswitches with advantageous PCM contact configurations overcome thedeficiencies in the art. From the above description it is manifest thatvarious techniques can be used for implementing the concepts describedin the present application without departing from the scope of thoseconcepts. Moreover, while the concepts have been described with specificreference to certain implementations, a person of ordinary skill in theart would recognize that changes can be made in form and detail withoutdeparting from the scope of those concepts. As such, the describedimplementations are to be considered in all respects as illustrative andnot restrictive. It should also be understood that the presentapplication is not limited to the particular implementations describedabove, but many rearrangements, modifications, and substitutions arepossible without departing from the scope of the present disclosure.

1-22. (canceled) 23: A radio frequency (RF) switch comprising: aphase-change material (PCM) and a heating element approximatelyunderlying an active segment of said PCM, said PCM and heating elementbeing situated over a substrate; a contact dielectric over said PCM; PCMcontacts comprising upper portions and uniform plate slot lowerportions; said uniform plate slot lower portions having a total plateresistance R_(PLATE), and a total plate slot interface resistanceR_(PLATE-INT); said upper portions having a total capacitance C_(UPPER)to said uniform plate slot lower portions, said PCM having a totalcapacitance C_(PCM) to said substrate: said uniform plate slot lowerportions resulting in significantly reducing a product of(R_(PLATE)+R_(PLATE-INT)) and (C_(uppper)+C_(PCM)), wherein said uniformplate slot lower portions are narrow plates so as to reduce said totalcapacitance C_(PCM) to said substrate. 24: The RF switch of claim 23,further comprising a thermally conductive and electrically insulatinglayer under said PCM. 25: The RF switch of claim 24, wherein saidthermally conductive and electrically insulating layer comprises amaterial selected from the group consisting of aluminum nitride (AlN),aluminum oxide (Al_(X)O_(Y)), beryllium oxide (Be_(X)O_(Y)), siliconcarbide (SiC), diamond, and diamond-like carbon. 26: The RF switch ofclaim 24, wherein a thickness of said contact dielectric issignificantly greater than a thickness of said thermally conductive andelectrically insulating layer. 27: The RF switch of claim 23, whereinsaid PCM comprises a material selected from the group consisting ofgermanium telluride (Ge_(X)Te_(Y)), germanium antimony telluride(Ge_(X)Sb_(Y)Te_(Z)), germanium selenide (Ge_(X)Se_(Y)), and any otherchalcogenide. 28: The RF switch of claim 23, wherein a contactuniformity support layer is situated over said PCM, wherein said contactuniformity support layer comprises nitride. 29: The RF switch of claim23, wherein a contact uniformity support layer is situated over saidPCM, wherein said contact uniformity support layer comprises a bi-layerthat includes oxide and nitride. 30: The RF switch of claim 23, whereina contact uniformity support layer is situated over said PCM, whereinsaid contact uniformity support layer significantly reduces said totalplate slot interface resistance R_(PLATE-INT). 31: The RF switch ofclaim 23, wherein said contact dielectric comprises a material selectedfrom the group consisting of SiO₂, boron-doped SiO₂, phosphorous-dopedSiO₂, Si_(X)N_(Y), fluorinated silicon dioxide, carbon-doped siliconoxide, and spin-on organic polymer. 32: The RF switch of claim 23,wherein said uniform plate slot lower portions and said upper portionsof said PCM contacts comprise a material selected from the groupconsisting of tungsten, aluminum, and copper. 33: The RF switch of claim23, wherein said uniform plate slot lower portions are narrow plates soas to reduce an area of said PCM such that said total capacitanceC_(PCM) to said substrate is reduced. 34: The RF switch of claim 23,wherein said uniform plate slot lower portions are narrow plates so asto connect to a top portion of said PCM without connecting to a sidewallof said PCM. 35: A radio frequency (RF) switch comprising: aphase-change material (PCM) and a heating element, said PCM and heatingelement being situated over a substrate, said PCM having a totalcapacitance C_(PCM) to said substrate; PCM contacts comprising upperportions and uniform plate slot lower portions; said uniform plate slotlower portions being narrow plates so as to reduce said totalcapacitance C_(PCM) to said substrate. 36: The RF switch of claim 35,wherein a contact uniformity support layer is situated over said PCM,wherein said contact uniformity support layer significantly reduces atotal plate slot interface resistance R_(PLATE-INT). 37: The RF switchof claim 36, wherein said contact uniformity support layer comprisesnitride. 38: The RF switch of claim 36, wherein said contact uniformitysupport layer comprises a bi-layer that includes oxide and nitride. 39:The RF switch of claim 35, further comprising a thermally conductive andelectrically insulating layer under said PCM. 40: The RF switch of claim39, wherein said thermally conductive and electrically insulating layercomprises a material selected from the group consisting of aluminumnitride (AlN), aluminum oxide (Al_(X)O_(Y)), beryllium oxide(Be_(X)O_(Y)), silicon carbide (SiC), diamond, and diamond-like carbon.41: The RF switch of claim 35, wherein said PCM comprises a materialselected from the group consisting of germanium telluride(Ge_(X)Te_(Y)), germanium antimony telluride (Ge_(X)Sb_(Y)Te_(Z)),germanium selenide (Ge_(X)Se_(Y)), and any other chalcogenide. 42: TheRF switch of claim 35, wherein said uniform plate slot lower portionsand said upper portions of said PCM contacts comprise a materialselected from the group consisting of tungsten, aluminum, and copper.